How To Write Extension Number On Business Card

Do I have to write my extension number on my business card? 3

update

I have to use an internationally understandable symbol ... a symbol that expresses ext. can change?

In addition to the main screw number. Extensions must precede extensions (of course without quotes).

Ah yes:

(123) 4567890 321 Extra

Shape of pneumatic extension

This page can help you.

Do I write my extension number on my business card?

I usually see it.
(123) 4567890 Extension 1234

I prefer x255 on business cards.

I'm also interested in learning more about it.